Pseudomonas aeruginosa is known to be naturally resistant against most of the antibiotics commonly used, and the use of antibiotics for the prophylactic treatment of infection due to bacteria is almost completely ineffective when the hosts are physiologically immature in immune response or in those cases where hosts are being treated by administration of medicines which decrease their immune protective mechanisms.
Since mink hemorrhagic pneumonia is endemic and caused by a single serotype strain, formalin-killed cells were prepared from cultures of the homologous serotype strain which had been isolated from mink which had died due to the endemic, with a view to developing a protective or preventive agent. For the purpose of protecting mink from the contagious disease, minks were immunized with the formalin-killed cells. However, the therapeutic effects were doubtful.
Actually, those antibiotics to which the bacteria are sensitive cannot readily be administered repeatedly to minks at 2-3 days' intervals because the number of minks to be processed is so great. The cost of the drug is another reason for the unsuitability of repeated administration of the drug to this species. Even when adopted, therapy by antibiotics is generally ineffective, because most of minks are kittens whose immune system is physiologically immature. Another reason is that a few administrations of the drug are not effective enough for preventing the natural development of the disease.
For bovine mammitis, there was a case in which antibiotics were administered continuously, but the effect achieved by administration for a lengthy period was actually not worth the cost of the drug. An acute case may be handled, but chronic cases could hardly be treated in most cases. The radical treatment of mastitis due to Pseudomonas aeruginosa cannot be achieved by antibiotic treatment alone and relapses of this infection occur after temporary success of the treatment.
On the other hand, immunization is an important factor for protecting hosts from infection due to Pseudomonas aeruginosa. As a vaccine, a thermostable O antigen of glycolipid derived from Pseudomonas aeruginosa is known, but this O antigen has the disadvantage that it exhibits a protective activity only against infection due to bacterial strains of the same serotype as that of the strain from which the vaccine was prepared.
As is evident a better method of protection of animals against infection by Pseudomonas aeruginosa is still needed.